Friday, May 22, 2009

Phenology and Invasive Species

I’ve been thinking about the relationship between phenology and invasive species this week as I’ve been pulling garlic mustard (Alliaria petiolata), one of the worst woodland invaders in the eastern U.S. Garlic mustard is a biennial herb; it forms a small rosette of leaves its first year, then bolts, flowers, sets seed, and dies its second year. Pulling it out at the right phenophase is the key to its control. It spreads by seed and a single plant can make thousands of seeds. It is crucial to pull it before those seeds are produced! The onset of flowering is the best time for control because garlic mustard is easy to spot (due to its white flowers), but no seeds have been formed. Right now is a great time to pull garlic mustard in the upper Midwest!

Another phenological observation about invasive species, at least in my part of the country, is that they often have a longer growing season than our native species. For instance common buckthorn and glossy buckthorn (Rhamnus cathartica and R. frangula), shrubs that invade woodlands in this region, are two of the first plants to leaf out in the spring and two of the last to drop leaves in the fall. This extended growing season may be one of the keys to their successful competitive ability. They can shade out anything growing under them and can capture sunlight and make sugar long before and after the oaks leaf out above. I’m wondering if this is a common phenomenon in species that invade forested areas. If you live near a woodland, please keep an eye out for what species green up first in the spring and drop their leaves last in the fall and let us know!

Lastly for a native species highlight, a colleague caught me in the hall this morning and said, “You have to go for a walk in the prairie, the shooters are out.” I must have looked a little confused before realizing she meant the shooting stars (Dodecatheon meadii). They are in full bloom right now in Chicago and are absolutely beautiful!

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